Published German patent specification DE-OS 36 37 666 discloses a phase- and amplitude-controlled loudspeaker with an arbitrary number of paths. The aim of the control is to linearize the frequency response (phase+amplitude) of an electroacoustic transducer. The electroacoustic transducer may be a single loudspeaker, but also an arrangement consisting of two or more loudspeakers. The closed-loop control system consists of a power amplifier, a passive crossover network, a summing amplifier, and one or more loudspeakers. The controlled variable is the voltage driving the loudspeakers, which is fed back to the input of the power amplifier. The feedback path contains an operational amplifier with a feedback network. The controlled variable can also be derived from other sensing elements (see FIG. 1).
The prior art controlled loudspeaker has the disadvantage that only negative voltage feedback is provided, which has little effect on the dynamic range of the loudspeaker. If the loudspeaker is driven at a frequency which is very close to a resonance point of the loudspeaker enclosure, the power radiated by the loudspeaker will vary widely, which, however, is hardly reflected in the drive voltage. Under such operating conditions, the prior art control has only little effect.